ON THE J-DEPENDENCE OF THE ISOTOPE SHIFT IN THE GROUND TERM OF GD-I

High-resolution laser-induced resonance fluorescence spectroscopy has been applied to investigate the isotope shift considering 19 lines in the isotope sequence 154Gd-158Gd, 160Gd. From this experimental data the level isotope shifts of the ground term a 9D of 4f75d6s2 were extracted and show a strong J-dependence. With a parametric description, including also higher-order isotope shift effects, this J-dependence was analysed and the following crossed-second-order isotope shift parameters (in MHz) were determined: Z5d(160-158)=19.2 (1.0), z5d(160-157)=32.2 (1.0), z5d(160-156)=36.6 (1.5), z5d(160-155)=47.1 (1.5), z5d(160-154)=62.3 (2.0). The normalisation of these parameters with the corresponding mean square nuclear charge radii delta (r2) and the spin-orbit Slater integral zeta 5d was constant for Gd I:z5d,norm=z5d /(delta (r2). zeta 5d)=6.0(0.6)*10−6 fm−2. This indicates a crossed-second-order effect of the spin-orbit interaction and the field shift operator. The magnetic and electric hyperfine structure splitting constants for the levels 9F2-4 and 9D2-6 of 4f 75d6s6p for 155Gd are also presented. © 1990 Elsevier Science Publishing Co., Inc.